In a typical inkjet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof.
An inkjet recording element typically comprises a support having on at least one surface thereof at least one ink-receiving layer. The ink-receiving layer is typically either a porous layer that imbibes the ink via capillary action, or a polymer layer that swells to absorb the ink. Transparent swellable hydrophilic polymer layers do not scatter light and therefore afford high image density and gamut, but tend to take longer time to dry. On the other hand, porous ink-receiving layers, which usually comprise inorganic or organic particles and a binder, can rapidly absorb ink droplets into the coating through capillary action, during the inkjet printing process, so that the image is dry-to-touch right after it comes out of the printer. Therefore, porous layers allow a fast “drying” of the ink and produce a smear-resistant image. However, such porous layers, by virtue of the large number of air-particle interfaces, tend to scatter light, which can result in lower densities of printed images.
Elements that comprise two distinct layers have been constructed which have an uppermost porous layer and an underlying swellable polymer layer. Such constructions suffer from poor image quality, however, as the rate of ink absorption in the upper porous layer via capillary action is orders of magnitude faster than absorption by ink diffusion into the swellable layer. This difference in absorption rates leads to unwanted lateral spreading of ink in the uppermost layer when the ink fluid reaches the interface between the layers. This unwanted lateral diffusion of the ink is a phenomenon known in the art as bleed.
Inkjet prints, prepared by printing onto inkjet recording elements, are subject to physical damage and environmental degradation. Dye-imaged inkjet prints on swellable media are especially vulnerable to damage resulting from contact with water. The damage resulting from the post-imaging contact with water can take the form of water spots resulting from deglossing of the top coat, dye smearing due to unwanted dye diffusion, and even gross dissolution of the image recording layer. On the other hand, dye-imaged inkjet prints on porous media are especially vulnerable to damage resulting from contact with atmospheric gases such as ozone. Ozone can bleach inkjet dyes resulting in loss of density. Pigment-imaged inkjet prints on porous media are relatively more robust against atmospheric gases, but can be easily smudged by rubbing the still moist surface of the pigmented image. Pigment-imaged inkjet prints are also subject to surface scratching and abrasion defects as the pigmented image generally resides on the media surface. To overcome these deficiencies, inkjet prints can be laminated. However, lamination is expensive, as it requires a separate roll of material.
Efforts have been made to avoid lamination and yet provide protected inkjet prints by providing an inkjet receiver having an uppermost fusible ink-transporting layer and an underlying ink-retaining layer, with respect to the colorant in the ink, typically a transportable dye. Fusing the upper layer after printing the image has the advantage of providing a protective overcoat, for water and stain resistance, and reducing light scatter for improved image quality.
For example, U.S. Pat. Nos. 4,785,313 and 4,832,984 relate to an inkjet recording element comprising a support having thereon a porous fusible, ink-transporting layer and a swellable polymeric ink-retaining layer, wherein the ink-retaining layer is non-porous. However, there is a problem with this element in that it has poor image quality due to bleed, as mentioned above.
EP 858, 905A1 relates to an inkjet recording element having a porous fusible ink-transporting outermost layer formed by heat sintering thermoplastic particles, and an underlying porous layer to absorb and retain the ink applied to the outermost layer to form an image. The underlying porous ink-retaining layer is constituted mainly of refractory pigments. After imaging, the outermost layer is made non-porous. There are problems with this element in that the ink-retaining layer remains light scattering and, therefore, fused prints suffer from low density. Also, the sintered outermost layer has poor abrasion resistance.
EP 1,188,573 A2 relates to a recording material comprising in order: a sheet-like paper substrate, at least one porous pigment layer coated thereon, and at least one sealing layer coated thereon. Also disclosed is an optional dye trapping layer present between the porous pigment and sealing layers. There are several problems with this element in that the binder in the sealing layer is water-soluble which degrades the water resistance of sealed prints. While the sealing layer is porous, the dye trapping layer is not, which leads to bleed and degraded image quality.
U.S. Pat. No. 6,695,447 to Wexler discloses inkjet media comprising a support having thereon, in order, at least one porous ink-receiving layer, a fusible porous dye-trapping layer (comprising fusible polymeric particles, a binder, and a dye mordant), and a fusible porous ink-transporting layer comprising fusible, polymeric particles and a film-forming hydrophobic binder. The particle sizes of the layers are chosen to provide a pore size hierarchy facilitating fluid transport from the ink transporting layer, through the porous dye-trapping layer and into the porous ink receiving layer. After printing and fusing, this element provides a print with sub-surface image protected from abrasion. An element with fewer layers would be preferred from a manufacturing standpoint. The latex dispersion of polymeric mordant may tend to reduce porosity upon swelling during printing.
EP 743,193 A1 discloses a transparent image-recording medium in which the printing and viewing surfaces are situated on opposite sides of the support and in which the recording surface comprises, in order from the transparent support, an ink-retaining layer and a liquid-permeable surface layer. This medium is designed to pass pigmented ink through the ink-permeable layer, but is not intended for viewing from the printed side. Moreover, the ink-permeable layer is not fusible.
U.S. Pat. No. 6,550,909 B2 discloses an inkjet recording element in which the frequency distribution of pore diameter of the pores of the porous fusible layer overlaps the frequency distribution of the particle size of the ink colorant, wherein the overlap portion is from 0.1% to 10% and, furthermore, wherein the pore diameter of all the pores of the porous layer is within a range of 10 to 300 nm. Most of the colorant particles are, therefore, larger than most of the pore diameters. Accordingly, a printing method employing this element with pigmented inks traps the ink-pigment particles within 5 microns of the surface of the recording medium. Images formed by surface-trapped particles, however, are subject to damage from abrasion of the print surface. In a comparative example, in which the overlap of pore size frequency distribution and ink particle size distribution was 58%, a poor optical density was obtained. In this example, the low optical density may be explained by assuming the ink pigment has penetrated deeply enough that light scattering reduces the optical density.
U.S. Pat. No. 6,811,253 discloses a method of printing to a medium comprising an upper layer that is capable of forming a upper protective layer. After printing, the medium is heated to fuse the upper layer to form a protective layer. The printed image is substantially retained within the upper protective layer. FIG. 1 of U.S. Pat. No. 6,811,253 shows the pigmented image distributed about evenly throughout the upper layer. The portion of the image formed by pigment particles at or near the surface is subject to damage through abrasion.